fix: implement generic Walk for gateway (#9938)

Walk() functionality was missing on gateway
implementations leading to missing functionality
for the browser UI such as remove multiple objects,
download as zip file etc.

This PR brings a generic implementation across
all gateway's, it is not required to repeat the
same code in all gateway's

cmd/gateway-main.go

@@ -45,6 +45,57 @@ var (
 	}
 )
 
+// GatewayLocker implements custom NewNSLock implementation
+type GatewayLocker struct {
+	ObjectLayer
+	nsMutex *nsLockMap
+}
+
+// NewNSLock - implements gateway level locker
+func (l *GatewayLocker) NewNSLock(ctx context.Context, bucket string, objects ...string) RWLocker {
+	return l.nsMutex.NewNSLock(ctx, nil, bucket, objects...)
+}
+
+// Walk - implements common gateway level Walker, to walk on all objects recursively at a prefix
+func (l *GatewayLocker) Walk(ctx context.Context, bucket, prefix string, results chan<- ObjectInfo) error {
+	walk := func(ctx context.Context, bucket, prefix string, results chan<- ObjectInfo) error {
+		var marker string
+		for {
+			// set maxKeys to '0' to list maximum possible objects in single call.
+			loi, err := l.ObjectLayer.ListObjects(ctx, bucket, prefix, marker, "", 0)
+			if err != nil {
+				return err
+			}
+			marker = loi.NextMarker
+			for _, obj := range loi.Objects {
+				select {
+				case results <- obj:
+				case <-ctx.Done():
+					return nil
+				}
+			}
+			if !loi.IsTruncated {
+				break
+			}
+		}
+		return nil
+	}
+
+	if err := l.ObjectLayer.Walk(ctx, bucket, prefix, results); err != nil {
+		if _, ok := err.(NotImplemented); ok {
+			return walk(ctx, bucket, prefix, results)
+		}
+		return err
+	}
+
+	return nil
+}
+
+// NewGatewayLayerWithLocker - initialize gateway with locker.
+func NewGatewayLayerWithLocker(gwLayer ObjectLayer) ObjectLayer {
+	return &GatewayLocker{ObjectLayer: gwLayer, nsMutex: newNSLock(false)}
+}
+
 // RegisterGatewayCommand registers a new command for gateway.
 func RegisterGatewayCommand(cmd cli.Command) error {
 	cmd.Flags = append(append(cmd.Flags, ServerFlags...), GlobalFlags...)

cmd/gateway-unsupported.go

@@ -31,22 +31,6 @@ import (
 	"github.com/minio/minio/pkg/madmin"
 )
 
-// GatewayLocker implements custom NeNSLock implementation
-type GatewayLocker struct {
-	ObjectLayer
-	nsMutex *nsLockMap
-}
-
-// NewNSLock - implements gateway level locker
-func (l *GatewayLocker) NewNSLock(ctx context.Context, bucket string, objects ...string) RWLocker {
-	return l.nsMutex.NewNSLock(ctx, nil, bucket, objects...)
-}
-
-// NewGatewayLayerWithLocker - initialize gateway with locker.
-func NewGatewayLayerWithLocker(gwLayer ObjectLayer) ObjectLayer {
-	return &GatewayLocker{ObjectLayer: gwLayer, nsMutex: newNSLock(false)}
-}
-
 // GatewayUnsupported list of unsupported call stubs for gateway.
 type GatewayUnsupported struct{}